Printers print in discrete amount of material to create an inidica on the page. The discrete amount of material is often referred to as a “dot.” The number of dots that can be printed without overlap defines the resolution of the printer. The smaller the “dot” the more dots that can be fit in an area prior to overlap (i.e., the dots can be spaced closer together). The term dpi or “dots per inch” refers to the number of dots that can be printed in a horizontal line. For example, 600 dpi means that the size of the mark made by the printer cannot be larger than 1/600 of an inch. This is referred to as the maximum resolution of the printer.
An image is represented in memory by an N ×N matrix of pixels. This matrix is subsequently mapped to a print head or print heads of the printer by the print controller. Although the printer has a maximum dpi, the print controller can cause the printer to print at a frequency which results in a lower dpi count than the maximum dpi of the printer. If the controller causes a printer, for example, to print a maximum of 300 dots per inch the resolution of the printed image will be 300 dpi, despite the fact that the printer might have a higher maximum resolution.
The position of a print target relative to the printer must be known in order for the printer to know when to print on the target. Sensors or control mechanisms are used to ascertain this relative position. Examples of control mechanism include a stepper motor or a positional encoder (e.g., an optical encoder). A stepper motor controls the position of the target whereas a positional encoder indicates the position of the target on a moving transport medium. When the position of the target matches the location where an indicia should be created, the print controller causes a mark to be placed on the target, at the position.
Frequently it is desired to print at resolutions other than the resolution enabled by the positional encoder coupled to the printer. For example, a barcode may need to be printed at a small size. A single bar in a barcode may only be one or two pixels wide and have a fixed ratio of wide bars to narrow bars, if the layout of the bar code does not align with the print resolution capabilities of a printer, barcodes that cannot be subsequently scanned may be printed. In addition, lower dpi printing uses less consumables such as ink, allowing less expensive printing. Thus, such a capability is highly desirable in applications such as high volume industrial printing.
In the past, printers used encoder translation to attempt to alter the native resolution of the printer. For example, if the pulse train generated by the encoder is sped up the resulting printed document is compressed. This technique has many limitations. Because the printer function itself is not changed, the parameters of the printer must be changed. For example, all elements of the printed indicia are compressed or expanded, even if this is not desired. Configuration parameters can also be affected since these parameters are frequently based on the accuracy of the incoming positional information.
What is therefore needed is a printer that allows flexible, simple configuration while maintaining correct print function across a large range of print resolutions.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers can indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears.